The reasons were not clear. It was not possible to determine whether a patient received a medication prescription, chose not to fill it, or actually took the drug, the investigators noted.

However, compliance was "suboptimal" for all patients, with and without kidney disease, and, with the exception of dialysis patients, kidney disease did not determine adherence to prescribed medications, Wolfgang C. Winkelmayer, M.D., of Brigham and Women's Hospital here, and colleagues reported online in the Clinical Journal of the American Society of Nephrology.

Furthermore, underuse of cardiovascular medication among patients with kidney disease did not appear responsible for the known increase in mortality after myocardial infarction in patients with reduced kidney function, the investigators said.

To determine whether kidney function affects adherence to recommended medications after an MI, the researchers undertook a retrospective cohort study of 21,500 patients ages 65 or older in New Jersey and Pennsylvania from 1995 through 2004.

Use of ACE inhibitors or angiotensin receptor blockers and statins was assessed within 30 days of discharge. Good adherence was defined as proportion of days covered >80% during the first year after discharge.

Overall rates of medication use were low for all patients. Within 30 days of discharge, 57.3% filled a prescription for a beta-blocker, 26.7% for a statin, and 44.1% for an ACE inhibitor or angiotensin receptor blocker.

After multivariate adjustment, compared with patients with no kidney disease, those with chronic kidney disease had a 22% lower adjusted use of ACE or angiotensin receptor blocker drugs, but similar rates of beta-blocker and statin use.

Patients on dialysis had even lower rates: 43% lower ACE or angiotensin receptor blocker drugs as well as 17% lower statin use. Although beta-blocker use was lower in crude analysis, after adjustment this association was no longer significant.

Kidney disease status did not determine one-year adherence to these drugs. Among all patients who filled a first prescription, adherence rates after one year were only 64% for beta-blockers, 57% for statins, and 54% for ACE or angiotensin receptor blocker.

For all three types of drugs, one-year adherence rates were similar for patients with and without chronic kidney disease. However, dialysis patients, who were less likely to start treatment with ACE or angiotensin receptor blocker drugs and statins, were less likely to continue beta-blocker treatment compared with chronic kidney-disease patients or those without kidney disease.

With the exception of lower ACE or angiotensin receptor blocker drug use in patients with chronic kidney disease, no difference was found between patients with and without kidney disease in their use of and adherence to these cardiovascular medications after myocardial infarction, the researchers said.

The study was limited by its retrospective design, the failure to include low-dose aspirin (no prescription needed), the absence of laboratory measures for kidney disease or function, which was determined from healthcare claims.

Postulated differences in medication use after an MI across levels of kidney function are unlikely to explain the observed differences in long-term outcomes for MI patients with kidney disease, the researchers wrote.

Because initiation of and adherence to recommended cardiovascular medications may not differ between patients with or without chronic kidney disease, other factors, including less state-of-the-art care, are likely responsible for the observed increase in cardiovascular risk among patients with low kidney function, the investigators said.

Detection of potentially modifiable factors that are specific to advanced kidney disease and the development of candidate therapies with proof of efficacy should be a top priority for the investment of private and public funds, especially given the high and increasing prevalence of kidney disease, Dr. Winkelmayer said.

This study was supported by an American Heart Association Scientist Development grant and a Norman S. Coplon Extramural Research Program Award from Satellite Research to Dr. Winkelmayer. No other financial conflicts were reported.

Reviewed by Zalman S. Agus, MD Emeritus Professor University of Pennsylvania School of Medicine

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